Production of anhydrous magnesium chloride



Aug. 14, 1945. A. BELcHETz PRODUCTION OF ANHYDROUS MAGNESIUM CHLORIDE Filed May 29, 1942 ATTORNEY Patented Aug. 14, 1945 UNITED STATES PATENT oFFlcrE PRODUCTION F ANHYDROUS MAGNESIUM CHLORIDE Arnold Belchetz, Kew Gardens, N. Y., asslgnor to The M. W. Kellogg Company, Jersey City, N. J., a corporation of Delaware Application May 29, 1942, Serial No. 444,981

8 Claims.

uble, distilling oif water with vapors of the liquid and leaving a non-aqueous solution of MgCl2 as the distillation residue.l Separation of solid anhydrous MgCl2 from the non-aqueous solution thereafter is accomplished by completely vaporizing the solvent. My present invention provides an alternative method of recovering dehydrated MgClz from such non-aqueous solutions. This method therefore, in its preferred embodiment, embraces my described process of heating a hydrous form of MgCl2 with a volatile non-aqueous liquid, distilling oil? water with vapors of the non-aqueous liquid and leaving an anhydrous non-aqueous solution of MgCl2 as the distillation residue and includes the step whereby anhydrous MgCl2 then is separated from its solution in the non-aqueous solvent by the addition of a precipitating agent which forms a solid complex with the MgCl2 that is insoluble in the non-aqueous liquid. The solid MgCl2 complex readily is separated from its association with liquid by filtration and the anhydrous MgCl2 then is recovered in a state of highest purity by dissociating the solid complex with a heat treatment.

The non-aqueous solvents which I preferto use in practising my invention are the saturated mono-hydroxy aliphatic alcohols and more speciiically'those alcohols of the latter type having atmospheric boiling points between 220 and about 350 F. In the following further description loi'- an exemplary embodiment of the invention with reference to the annexed drawing the use of such analcohol will be assumed. As will be understood by those skilled in the art, however, other solvents can be used. I particularly prefer the amy] alcohols or pentanols as sol,

vents. Hexyl alcohols can be used but because of their generally higher cost are not conducive .to anveconomical operation. Exemplary operating conditions are'given for the use ofisoamyl 5. It will dissolve upwards of 16% alcohol in the speciilc embodiment of the invention hereinafter described. The significant properties of isoamyl alcohol are asfollows:

1. Its boilingpoint is 267 F. l

2. It forms a. constant boiling mixture with water consisting of about 58% alcohol-and about 42% water, and having a boiling point of 203 F.

` 3. It dissolves water to the extent of about 10% by weight at '100 F. 4. It is soluble in water-to the extent of about 2% by weight at 100 F.

MgCl2 at its boiling point. The precipitating agent which I prefer to use for separating the MgCl2 from the non-aqueous liquid is anhydrous ammonia. I prefer further tc use anhydrous ammonia in the vapor phase since its use in this phasepermits the process of my invention to be carried out in a system not requiring refrigeration and under condition more suitable and more conducive to an economical operation, as will become apparent in vthe following description.

The annexed drawing is a diagrammatic flow arrangement of an exemplary embodiment of the invention 4wherein items of equipment are conventionally shown and from' which self-evident necessaries, such as pumps, valves and the like have been omitted for greater clarity. It is understood that reference to the drawing is by way of example only as the invention is capable of other embodiments and is not to be restricted to the physical limitations of the apparatus indi-v cated in the drawing. y. A

The operating step rst to be described is essentially a distillation step and could, -if desired, be carried out as a bat/ch operation.' For greatest eiiiciency, however, it is Ipreferable to employ continuous fractionating equipment and Ato supply thefeed inthe form of a hot aqueous solution f of MgCl: containing the minimum amount of water; that is, to supply MgClzHaO dissolved in little more than its own water-of' 'crystallization Such-a solution may be obtained from a more dilute one by conventional vaporvization methods or in other ways depending upon the original source ot the MgCl2.

In the drawing an aqueous MgCl2 solution is by weight of l taken from any available source and introduced into line I. An alcohol-water mixture derived from a subsequent step of the process is introduced into' line `I through line 2, and anhydrous alcohol derived from still another step of the desired, the small amount of alcohol accompany- .i

ing the Withdrawn slurry is recovered by vaporization and returned to the process. It will be seen that my method of preparing pure anhydrous MgCl2 has the advantage initially of accomplishing the removal of soluble salts such as are likely to be associated with MgCl2 obtained by fractional crystallization of brines. In fact, when the source of MgCl2 is a mixture of dissolved salts, little or no purification thereof prior to dehydration may be required other than that provided by the above-mentioned precipitation. The sedimentation drum 4 is alternatively replaced by a filter, if desired.

The MgClz-water-alcohol solution from which insoluble impurities have been removed, is passed throughline 6to a preheater 'I wherein it is heated preferably to its boiling point. It is then,

introduced into an intermediate section of a distillationcolumn 8. The latter can be of conventional design, embodying fractionating bubble trays, baies, packing or the like. A reboiler coil 9 is situated in the base of column 8 to maintain a bottom temperature of approximately 267 F. The bottom temperature Will, however, because of the boiling point raising eiiect of the dissolved MgCl.` with alcohol be somewhat higher than 267 F. and the exact temperature will depend upon.

how nearly saturated a solution is withdrawn from the bottom of the column. A water cooled reflux condenser I0 is located at the top of column 8 to maintain a temperature which in the present instances should be 203 F.

In column 8 the feed material is fractionated into absolute isoamyl alcohol as the higher boiling bottom product and a constant-boiling mixture of water and isoamyl alcohol'a's the lower boiling top product. The MgCl2, being nonvolatile, remains in the liquid owing down through the column and is withdrawn from column 8 inan anhydrous condition, dissolved in the absolute alcohol, by means of line Il. It is preferable to provide suilicient excess alcohol in theglower section of column 8 and in line II to avoid any possibility of crystallization at these points.

In distillation column 8 the function of the reboiler c oil 9 and the vapor-liquid contact in the lower portion of the column is-to expel all water from the feed mixture, so as to make possible the Withdrawal of an anhydrous alcohol solution as bottom product.l As the water vis vaporized and expelled from the feed, mixture, there is` vinevitably a substantial vaporization of alcohol also, and the function of the upper section of the column and the reflux-condensing coil I0 is to prevent, as far as possible,'the escape of alcohol with the wateriin the' overhead vapors. It

I prefer to employ in practising my invention all form constant-boiling mixtures with water; that is to say, in distilling mixtures of these alcohols with water, it is not possible to produce both anhydrous alcohol land alcohol-free Water from any one alcohol-water mixture. If `the mixture to be distilled contains more water (less alcohol) than the constant-boiling mixture, then it will not be possibleto produce anhydrous alcohol as a product. The alcohol will be concentrated to the proportion in which it exists in the constant-boiling mixture, and the excess water will be produced as a bottom product, free from alcohol if the fractionation is sumciently precise.

If on the other hand the mixture contains less water (more alcohol) than the corresponding constant-boiling mixture, then anhydrous alcoholr may be withdrawn as a bottom product and the constant-boiling mixture will be the top product, providing sufilciently precise fractionation is effected. Inasmuch as the vlatter situation necessarily must obtain in practising my invention, i. e., anhydro'usalcohol must be one of the distillation products, it is necessary vto add to the initial MgCl2 solution that quantity of alcohol which will be distilled off with the water to be removed, in a constant-boiling mixture. Also, it

is necessary to add alcohol in excess of the latter quantity, to act as a solvent for the anhydrous magnesium chloride and prevent it from being left as a solidwhen the water and the lrst quanthat the column must contain a suilicient number of plates or the like if fractionation of excess alcohol from the top product is to be eiected.

The overhead vapors from column 8 are passed through line' I2 into line I3 and are cooled suitably to about 100 F. and liquefied in condenser I4, the condensatethen being passed through line I5 to a. settler or decanter It. Isoamyl alcohol is soluble in water at100 F. to an extent vof about 2% by weight, and correspondingly water is soluble in isoamyl alcohol at 100 F. to the'extent of about 10% by weight. Hence, in the decanter I6 there will be a separation of the condensate into two layers, the upper layer being mostly alcohol and the lower layer mostly water. As the water layer contains less than the constant boiling mixture proportion of alcohol,

it is possible, as hereinbefore explained, to .ob' tain from it by fractionation an alcohol-free nwater as a bottom product. The lower or Water layer is withdrawn from decanter I6 through line II and rectiiied in redistillation column I8. Reboiler heat ,is supplied to column I8 by steam heated reboiler coil I8, the bottom temperature being substantiallyv the boiling point of water,

`212 F. The top of the redistination commi; is

again is maintained at 203 F., the boiling point of the constant boiling mixture of isoamyl alcohol and water, by means of reflux condensing coil 20. Vapors from column I8 pass through line 2l t0 be combined with vapors from column so happens that isoamyl and those alcohols which '15 8 in line I3 whence they travel in admixture'.-v

"cooled to substantially 100 one with the other to the condensation and decantation steps.

' 'I'he upper layer of liquid in decanter It is withdrawn .through line 2 and introduced into the previously mentioned feed line I. much as this layer will at 100 mixture of roughly 90% alcohol and the distillateA vapors in column 8 will contain 42% water, each pound of alcohol supplied to column 8 from decanter I6 will be capable of carrying overhead about 0.6 pound of water in addition to that water which enters the column with it, assuming eilicient fractionation. It is understood 'that the anhydrous recovered from another stage inv will be described later, and returned through line l supplies the proportion o f alcohol necessary to act as a solvent for the anhydrous MgCl2, and that the isoamyl alcohol as is recovered by decantation is in quantities sufficient for the removal of water from the aqueous feed. 'I'here are, therefore, two closed continuous alcohol cycles which supply a suitable proportion oi alcohol to line I for the lproper invention. Unavoidably small from the system are made up tions.

'Ihe water removing capacity of the alcoholrich liquid supplied to feed line I from decanter I6 is F. consist of a 'losses of alcohol by periodic addiin that liquid and the percent water in the constant-boiling mixture. The former ligure is, as 'previously stated, ap-

that of the absolute alcohol itself. It is entirely possible and within the scope of the in.-

smaller volume of -vapors taken overhead.

Referring again to the anhydrous distillation residue removed from this solution is contacted with ammonia gas which enters line II spectively. I'he ammonia is thoroughly intermixed with the distillation residue in line` II and the intimately mixed mixture thereafter is F. in cooler 2lA to precipitate solid particles of plex from the isoamyl alcohol.

a solution of ammonia in alcohol, enters ammonia stripping column 2l at an infermediate point through line 21. Column 2l can be conventional in design, having a steam reboiler coil 26 located at the bottom and a water cooled reflux condensing coil 30 at the top. In column Inas-n column I through line II,

l111g P01111: of the alcohol and 10% water,

which in the present instance is about 267 F. and by keeping the top oi column 28 at a temperature of about 120 F. by means oi' coil I0 to prevent the escape of alcohol with the overhead ammonia vapors. I'he vapors of ammonia pass out through line 22 to be combined with the anhydrous distillation residue through line 3 to line I for readmixture with additional quantities of the hydrous MgCl2 feed, as previously described.

The solid MgClzNI-I; precipitate, removed on filter 26, is picked up immediately by screw feeder mechanism 3l and carried into surge drum I2 where a stream of hot ammonia vapors entering at the bottom from line 3l strips the solid MgCl2.6NH3 oi' residual traces oi' alcohol. 'I'he exit vapors from this treatment consisting of ammonia and alcohol leave surge drum 32 through line 23 for introduction into line I I, as heretoforel thus stripped particles of the MgCl2-ammonia complex are picked up from the bottom of surge drum 32 by screw feeder mechanism 34 and discharged into a stream of ammonia into the ilred heater 36. The hot ammonia vapors entering surge drum 32 may contain suilicient heat to partially decompose. the MgClzNHla to a lower form ofthe MgCls-ammonia complex such asMgClaANH: or MgClz.2NHa

is raised to a point ranging from about 700 to 900 F. and, upon being heated to an elevated temperature of this order, the complex breaks down progressively to MgClnANI-Ia, M8Cl2.2NH3, lmNH: and finally to pure MgCl2 and pure Thus by a simple heat treatment the coming additional quantities of the MgCl2-ammonia complex througnheater Il. The supply of pure anhydrous MgCl: which accumulates in the bottom of settler 38 is removed therefrom by screw conveyor mechanism 4I and disposed of as desired via product outlet line 42.

I claim: 1. A method ofseparaung anhydrous magnesium chloride from a solution of anhydrous magnesium chloride in an anhydrous mono-hydroxy saturated aliphatic alcohol which comprises adding anhydrous ammonia thereto to precipitate an insoluble solid complex of magnesium ammonia passes chloride 'and ammonia from said solution and thereafter separating the anhydrous magnesium chloride from said complex.

2. A method as in claim 1 wherein said monohydroxy saturated Ialcohol is an isoamyl alcohol.

3. In a method of separating anhydrous magnesium chloride from its solution with an anhydrous,` mono-hydroxy saturated aliphatic alcohol the improvement which comprises adding anhydrous ammonia to said alcohol solution to precipitate anv insoluble solid magnesium chloride-ammonia complex therefrom, separating said complex from saidalcohol and thereafter heating the solid complex to remove the ammonia therefrom whereby the anhydrous magnesium chloride is recovered as the residue.

4. In a method of separating magnesium chloride from its solution with an anhydrous monohydroxy saturated aliphatic alcohol the improvement which comprises passing vapors of anhydrous ammonia through said solution to precipitate an insoluble solid complex of magnesium chloride and ammonia therefrom, separating said complex from said alcohol and thereafter heating the saturated'complex to a temperature lbetween '100 and 900 F. to recover anhydrous magnesium chloride therefrom.

5. In the method of preparing anhydrous mag- V nesium chloride from hydrous forms thereof consisting of heating a hydrous lform of magnesium, chloride with a mono-hydroxy saturated aliphatic alcohol and distilling off all of the water in said hydrous material in admixture with vapors of said alcohol thereby forming as a distillate residue an anhydrous solution of magnesium chloride in said alcohol and then separating anhydrous magnesium chloride from said solution, the improvement which comprises mixing anhydrous ammonia tvith said distillate residue to precipitate therefrom an insoluble magnesium chloride-ammonia compound, removing the magnesium chloride-ammonia compound from its associationwith said alcohol and dissociating said compound into anhydrous'magnesium chloride and ammonia to recover the magnesium chloride therefrom.

6. In the method of preparing anhydrous magnesium chloride from hydrous forms thereof consisting of heating a hydrous form of magnesium chloride with an lsoomyl alcohol and dlstilim'g oil' all of the water in said hydrous material iii y admixture with vapors forming as a distillate residue an anhydrous solution of magnesium chloride in said alcohol and then separating anhydrous magnesium chloride from said solution, the improvement which comprises mixing anhydrous ammonia with said distillate residue to precipitate therefrom an insoluble magnesium chloride-ammonia compound.

removing the magnesium chloride ammonia compound from its association with said alcohol and dissociating said compound into anhydrous magnesium chloride and ammonia to recover the magnesium chloride therefrom.

7. In a method of preparing anhydrous magnesium chloride from an aqueous magnesium chloride solution which comprises. mixing said solution with a mono-hydroxy saturated aliphatic alcohol-boiling above 220 F. and distilling off all water from the mixture together with a portion of the alcohol to form an anhydrous solution of magnesium chloride in alcohol .and separating the magnesium chloride, the improvement which comprises passing vapors of ammonia into said alcohol solution to precipitate an insoluble solid complex of magnesium chloride and ammonia therefrom, separating said solid precipitate and then heating the separated precipitate to recover anhydrous magnesium chloride free from ammonia.

' 8. A method of separating anhydrous magnesium chloride from a solution of anhydrous magnesium chloride in an anhydrous monohydroxy saturated aliphatic alcohol which comprises adding anhydrous ammonia thereto to precipitate an insoluble solid complex oi magnesium .chloride and ammonia from said solution, separating said solid complex, blowing hot vapors of ammonia through the separated complex to drive off residual amounts of alcohol,

conveying particles of the alcohol-free complex in a stream of ammonia vapors through a heated zone of restricted cross-sectional area to dissociatevsaid particles into anhydrous magnesium chloride and ammonia, recovering anhydrous magnesium chloride from the products of dissociation and returning portions of the ammonia glontent of said products of dissociation to said drying and heating zones.

ARNOLD BELQHETZ.

of said alcohol thereby l 

